The present invention relates to a method and an apparatus for purifying an oxygen containing gas. More specifically, the present invention relates to a method and an apparatus for purifying an oxygen containing gas by which not only an air can be disinfected or deodorized and an air which is preferably used for clean rooms can be purified, but also hardly decomposable organic compounds contained in an air and inorganic air pollutants such as NOx, SOx, CO, and ammonia can be decomposed to make them harmless.
As methods for purifying an oxygen containing gas (hereinafter, sometimes referred to as an air for brevity), (1) a method wherein ozone is generated in an air by using an ozone generating device and then diffused, (2) a method wherein disinfection of an air is performed by using a germicidal lamp, and (3) a method wherein an HEPA (high efficiency particulate air) filter or a chemical filter which is installed for clean rooms or others is used are heretofore known.
However, there are such problems that the ozone diffusing method of (1) emits ozone which is harmful to human bodies; that the method of (2) can not instantaneously disinfect a large quantity of air since the method principally uses ultraviolet rays of a wavelength of 254 nm and thus does not form active oxygen, and the method of (2) does not have an effect in the shadow portions of an germicidal lamp; and further that the method of (3) using an HEPA filter only captures bacteria with the filter, does not have an effect of disinfection, and has defects such that when a chemical filter is used, a long time is required for exchanging the filter whereas a disinfecting effect can be produced, and when a time appropriate for exchanging the filter was past, bacteria propagate contrary to expectations. Besides, it was impossible by the methods described above to decompose and remove hardly decomposable organic compounds, for example, chlorine containing aromatic compounds when these compounds are contained in an air to be treated.
An object of the present invention is to resolve the problems in conventional technology described above and to provide a method and an apparatus for purifying an air by which a large quantity of an air to be treated (hereinafter, sometimes the words xe2x80x9cto be treatedxe2x80x9d are omitted for brevity) can instantaneously be disinfected, deodorized, and purified, and an air which is harmless to men and beasts can be regenerated. Another object of the present invention is to provide a method and an apparatus for purifying an air by which chains between carbon atoms, for example, single bonds, double bonds, triple bonds in hardly decomposable organic compounds can be severed to decompose the compounds into low molecular weight compounds such as carbonic acid gas and water even when the hardly decomposable organic compounds are contained in an air.
The method for purifying an air according to the present invention is characterized by radiating ultraviolet rays to an air in the presence of a photocatalyst comprising titanium oxide. More specifically, the method of the present invention for purifying an air comprises a first step for radiating ultraviolet rays of a short wavelength of, for example, 110 nm or longer, but shorter than 200 nm to an air to generate ozone in the air, a second step for further radiating ultraviolet rays of a medium wavelength of 200 nm or longer, but shorter than 300 nm to the air treated in the first step to form active oxygen, and a third step for still further radiating ultraviolet rays of a long wavelength of 300 nm or longer, but shorter than 380 nm to the air treated in the second step to convert the active oxygen into oxygen molecule in ground state, at least the second and/or the third step being conducted in the presence of a photocatalyst. The step for generating ozone in an air is not limited to a step wherein the ultraviolet rays described above are radiated, but includes a step wherein silent discharge is conducted in an air.
The photocatalyst generally comprises particles of a photo-semiconductor such as titanium dioxide. When desired, the photocatalyst comprises particles in which fine particles of a metal such as silver are supported as an electrode on the particles of the photo-semiconductor. As the particles of a photo-semiconductor, particles of titanium oxide of a tetragonal crystal system (anatase type or rutile type) well known in the art can be used, but particles of titanium oxide of an orthorhombic crystal system or particles of titanium oxide of an orthorhombic crystal system supporting fine particles of another metal are desirably used in particular. As the particles of titanium oxide of an orthorhombic crystal system, particles of brookite are most desirable. Particles of titanium oxide of a different crystal system or particles of a photo-semiconductor other than titanium oxide may be used together.
In the method of the present invention, the air treated in the third step described above is preferably dried by further irradiating the air with rays (usually or mainly infrared rays) radiated from an infrared lamp and with rays (mainly near infrared rays) radiated from a halogen lamp. In this connection, while the method of the present invention can be applied for purifying various gases containing oxygen, the method is most advantageously applied for purifying an air.
The apparatus of the present invention for purifying an air comprises a first treating room having means for supplying the air and a device for generating ozone in the air, for example, a device for radiating ultraviolet rays of a short wavelength of 110 nm or longer, but shorter than 200 nm to the air, a second treating room connected to the first treating room and having a device for radiating ultraviolet rays of a medium wavelength of 200 nm or longer, but shorter than 300 nm to the air supplied from the first treating room, a third treating room connected to the second treating room and having a device for radiating ultraviolet rays of a long wavelength of 300 nm or longer, but shorter than 380 nm to the air supplied from the second treating room, and means for discharging the air treated in the third treating room outside the apparatus, the second and/or the third treating room having a photocatalyst.
As the photocatalyst used in the apparatus, the same as or similar to the apparatus described above with respect to the method of the present invention can be used.
The apparatus of the present invention is preferably provided, in the third treating room described above, with a drying room wherein a portion for irradiating an oxygen containing gas with rays radiated from an infrared lamp and a portion for irradiating the oxygen containing gas with rays radiated from a halogen lamp are installed.
While the apparatus of the present invention can also be applied for purifying various gases containing oxygen, the apparatus is most advantageously applied for purifying an air.